Control of disseminated M. avium infections is complicated by the refractory nature of this organism to widely used antimycobacterial agents. Thus there is an urgent need to develop new and effective therapies for such infections. At present our ability to derive new chemotherapeutic agents or immuno-modulatory treatments is hampered by the absence of a molecular definition of pathogenicity and drug resistance in this organism. A universally observed phenotypic characteristic of M. avium is its ability to exhibit several well-defined colony morphologies. Moreover, a clear correlation exists between these morphological variants and their relative virulence. There is also strong evidence of a relationship between these morphotypes and drug resistance. Thus, the goal of this project is to exploit the morphological variations of MAC strains to address issues of drug susceptibility and pathogenicity at the molecular level. Colony morphotypes of M. avium serovar 2 have been well defined in terms of glycopeptidolipid (GPL) expression, differential protein expression, pathogenicity, and drug susceptibility patterns. Thus, this strain in its various forms will serve as a tool to define the biochemical and genetic markers that distinguish virulent (drug resistant) and avirulent (drug susceptible) MAC. Specifically, the applicants will continue defining the genes involved in GPL biosynthesis and characterize SmT 66, a protein associated with the virulent, smooth transparent colony morphotype. They will also characterize other differences in protein, carbohydrate and lipid profiles between virulent and avirulent morphological variants. Identification of the genes corresponding to morphotype-specific components, and their use in the construction of mutant and recombinant M. avium strains, will permit genetic analyses of the basis for survival within macrophages, and drug susceptibility. Similar studies of microbial pathogens displaying morphotype-associated virulence provide a paradigm for the proposed project. The ultimate goal is to provide direction for the development of novel drug strategies that effect a "double whammy" against the organisms by targeting the expression of both virulence and drug resistance.